1. Field of the Invention
The present invention relates to an input device which measures changes of a rotation angle to use the measured changes as an input signal, and a method for the same. More particularly, the present invention relates to an input device which measures a rotation angle using a magnetic sensor and generates an input signal corresponding to the measured rotation angle in order to prevent generation of a wrong input signal by ignoring the rotation angle measured when the input device is tilted by more than a certain angle, and a method for generating the input signal.
2. Description of the Related Art
Recently, as electronic technology and network communication technology develops, the use of a variety of portable electronic devices such as a mobile phone, a personal digital assistant (PDA) and a notebook computer has been increasing. Many of these electronic devices are equipped with various functions such as games, text message service and notepads, and users can utilize the functions through an input means provided with the devices. Since mobile contents services have become more common, assorted games enjoyable through the mobile phones have become very popular. However, these portable electronic devices have a limitation in hardware compared to a personal computer (PC) and other game machines, which can comprise a variety of input means such as a mouse, a joystick and a keyboard.
Therefore, key input means such as numeric keys and direction keys are used in the portable electronic devices. A voice recognition function had once been developed and popularized, in which a certain word is recorded in a memory in the form of voice so that various operations are performed through the voice recognition as a user speaks the word. However, due to incorrectness and inconvenience, the voice recognition function is rarely used in the portable electronic devices.
In order to overcome the hardware limitation, an input device has been used, which measures a rotation angle of the portable electronic device and generates an input signal corresponding to the rotation angle. The input device usually comprises a built-in gyrosensor to measure the rotation angle and generate the corresponding input signal. When the user wants to move a cursor in a certain direction while searching a screen of the portable electronic device, the user orients the device in the desired direction. By this, the rotation angle for orientation is sensed by the gyrosensor, and the cursor is moved to the rotated direction or the counter-rotated direction.
The gyrosensor measures a rotation angle. More specifically, the gyrosensor measures the rotation angle first to calculate a rotation amount of the portable electronic device, and integrates the measured rotation angle with respect to time, thereby calculating a moving distance.
By using the rotation angle for the input signal, even minute operations not performable by the simple key operation, can be implemented. However, since the gyrosensor performs the integral operation several times to obtain the rotation angle, an integral constant is caused, and an error is generated as the integral constants are accumulated. More specifically, although the user rotates the portable electronic device by a certain angle and stops rotating, the gyrosensor considers it as continuous rotation due to the integral constant and continuously generates the input signals corresponding to the rotation angle. As a result, resolving power of the input device is deteriorated and there is a lack of precise control.
Alternatively, a geomagnetic sensor capable of measuring a rotation angle can be employed in the input device. The geomagnetic sensor senses degree and direction of geomagnetism that humans cannot sense. A geomagnetic sensor using a fluxgate is called a fluxgate geomagnetic sensor.
The fluxgate geomagnetic sensor uses a material of high magnetic permeability, such as permalloy, as a magnetic core to apply excitation by a driving coil and measure second harmonics. The excitation is proportional to an external magnetic field, using magnetic saturation and a non-linear magnetism of the magnetic coil, thereby measuring degree and direction of an external magnetic field.
The fluxgate geomagnetic sensor, introduced in the late 1930's, is superior to other types of geomagnetic sensors in sensitivity, economy and compactness. Further, the fluxgate geomagnetic sensor is power-saving and superior in long-term stability. Therefore, the fluxgate geomagnetic sensor is most widely used for civilian requirements and military affairs, for example, detection of weak magnetic field, measurement of terrestrial absolute direction, lode detection, mark detection, control of posture of an artificial satellite, and space exploration. Even today, research for improving the fluxgate is underway.
Recently, a micro-fluxgate sensor has been under development for low power consumption, using a micro electromechanical system (MEMS) technology.
Such micro-geomagnetic sensor is used in miniaturized portable electronic devices and is advantageous in higher resolving power and less errors caused by the accumulated integral constant.
In order to measure the rotation angle using the geomagnetic sensor, the geomagnetic sensor such as the fluxgate sensor is driven first, and an azimuth is measured by measuring voltage induced to the geomagnetic sensor. By comparing the azimuth to a previously measured azimuth, the rotation angle is obtained.
However, when the portable electronic device having the geomagnetic sensor is tilted, the azimuth can not be correctly measured. Therefore, when the horizontalness of the portable electronic device is not maintained, the geomagnetic sensor is not appropriate for use in the input device.
The horizontalness of the geomagnetic sensor is expressed by a pitch angle and a roll angle. When the pitch angle and the roll angle are both 0°, the geomagnetic sensor is considered to be horizontal. FIG. 1 illustrates an X-axis and a Y-axis perpendicular to each other, which are standards for measuring the pitch angle and the roll angle in a general portable device 10, on which are disposed a geomagnetic sensor 11 and an accelerometer 13. When the portable device 10 rotates about the X-axis, an angle between the portable device 10 and the Y-axis is the pitch angle, and when the portable device 10 rotates about the Y-axis, an angle between the portable device 10 and the X-axis is the roll angle. That is, the X-axis and the Y-axis, respectively, become a roll-axis and a pitch-axis.
FIG. 2 is a schematic view of a mobile phone 20 including the geomagnetic sensor 11, for explaining a method for playing a game using the mobile phone 20. As shown in FIG. 2, if a user is playing a car-racing game, the user can control a moving direction of a car displayed on a screen 25 by rotating the mobile phone 20 in a desired direction.
For this, a yaw angle is measured, and an input signal is generated according to change of the yaw angle. As shown in FIG. 2, the yaw angle refers to a rotation angle with respect to a Z-axis which is perpendicular to a plane comprising the X-axis and the Y-axis. General input devices using the geomagnetic sensor measure the yaw angle, that is, the azimuth and compare it to the previous azimuth. The change degree of the azimuth is considered to be the rotation angle. After the rotation angle is measured, an input signal is generated so that a cursor is moved in the rotation direction in proportion to the rotation angle. However, when the mobile phone 20 is not put on a level surface such as a desk during the game, the mobile phone 20 may be tilted, and in this case, fluxgate voltage output from the geomagnetic sensor 11 may change. Therefore, even when the mobile phone 20 is not rotated but only tilted, the mobile phone 20 recognizes this as rotation and generates the input signal. Accordingly, an unexpected input signal may be generated. Therefore, this kind of game is not enjoyable through the mobile phone 20.
There has been much research on methods for compensating an influence of tilt, to measure the rotation angle more precisely. However, since the input device should react immediately according to the input signal, if a process of tilt compensation is included, the reaction is delayed due to an operation load.